Ajax: use anchor tag for parsing urls

This PR changes the Ajax URL parsing from using a regex to using an anchor tag. This should be simpler and more reliable.

Fixes https://github.com/jquery/jquery/issues/1875
/cc @dmethvin
Indent one extra level for statements too long to fit on a line. Never indent to align code. http://contribute.jquery.org/style-guide/js/#multi-line-statements